Um...
This.
I was referring to the utility, not the format. While I use the 7Zip utility I rarely use the 7Zip container format. Yes, irony..
It's in the insiders program ISO releases. It's been present for a little bit. NOT a welcome type of functionality IMO.
Though it's not talked about in this
build, it does seem to be included and the functionality to unpack RAR and other less common container file types is present. It works the same way Windows handles normal contain files, which is VERY clunky and cumbersome, thus my original comment.